Via Gaussian 98, calculations have been carried out as B3LYP/6-31G** basis sets and the predominant tautomers of benzalbarbituric acid (BenzalBA) have been defined taking in consideration the energy of the density functional theory. The electronic transition energies have been calculated for the possible tautomers by the configuration interaction between the ground configuration Eigenfunction and the excited configuration Eigenfunctions explaining the absence of the relative intensity change in the UV spectrum by the heat effect as a result of the coincidence of the transition energies of the possible tautomers. The electronic spectra (UV–visible) were scanned for BenzalBA in different solvents of different polarities to determine the Einstein transition probabilities, dipole strengths, oscillator strengths, lifetime of the excited states and extinction coefficients. The hydrogen bonding and the orientation energy of the polar solvent molecules toward BenzalBA molecule were determined from the spectral studies in mixtures of polar and non-polar solvents. Some complexes were prepared from BenzalBA with some divalent metal ions, i.e. Fe++, Zn++ or Cu++. Their structures have been confirmed by elemental analysis, mass spectra, 1H NMR spectra, atomic absorption spectra and UV–visible spectra. It has been concluded that the structures of the complexes have the C2h point group symmetry in which two BenzalBA moieties are chelated to any one of the metal ions Fe++, Zn++ and Cu++.

A method has been developed to synthesize metal and metal oxide nanostructures in high yields on the surface of SiO2/Si substrate. In this method, starting materials in a covered alumina crucible are thermally evaporated under a high vacuum or a low pressure of ambient air. Spherical gold nanoparticles with a size of 15nmand nanowires with a diameter of 70nmwere synthesized. SnO2 rough microwires, smooth nanowires, and nanoknives were synthesized by using Sn granules, SnO powder, and SnO2 powder as source materials, respectively. The microwires showed a quadrangular cross section and a length of several microns, while the nanowires showed a circular cross section and approximately the same length. The effects of source temperature and deposition time on nanostructure growth were studied. X-ray diffraction patterns suggested that the as-synthesized products consisted of crystalline nanostructure. Nanocomposite gas sensors on the base of noble metal and metal oxide were fabricated. These SnO2 nanowire gas sensors showed a reversible response to dilute NO2 gas at operating temperatures ranging between room temperature and 300 ◦C even at high concentrations. The results demonstrated that gold doping improved the sensor response.

Electrodes with micro-gaps are fabricated by using dc-sputtering and FIB techniques. SnO2 nanowires are deposited on the micro-gap (1–30 m) by suspension dropping method to fabricate a micro-gas sensor. The sensing ability of various SnO2 micro-gap sensors is measured. A comparison between sensors reveals that the short-gap electrode has numerous advantages in terms of reliability, high sensitivity and detection of low concentrations of NO2, while the large-gap electrode is relatively sensitive for high concentrations. Conductance measurements are carried out at different surface temperatures and NO2 concentrations in order to investigate the effects that the gap size has on the overall sensor conductance. The results suggest that the interface between the electrode and sensitive layer has a very important role for the sensing mechanism of tin dioxide gas sensors.

SnO2 microwires, nanowires and rice-shaped nanoparticles were synthesized by a thermal evaporation method. The diameters of microwire and nanowire were 2mand 50–100 nm, respectively, with approximately the same length (∼20m). The size of nanoparticles was about 100 nm. It was confirmed that the as-synthesized products have SnO2 crystalline rutile structure. The sensing ability of SnO2 particle and wire-like structure configured as gas sensors was measured. A comparison between the particle and wire-like structure sensors revealed that the latter have numerous advantages in terms of reliability and high sensitivity. Although its high surface-to-volume ratio, the nanoparticle sensor exhibited the lowest sensitivity. The high surface-to-volume ratio and low density of grain boundaries is the best way to improve the sensitivity of SnO2 gas sensors, as in case of nanowire sensor which exhibited a dramatic improvement in sensitivity to NO2 gas.

Different compositions of Bi5GexSe95
x (x ¼ 30, 35, 40 and 45 at %) thin films were deposited onto cleaned glass substrates by thermal evaporation method. The structural characterization revealed that, the as-prepared films of x ¼ 30, 35 and 40 at. % are in amorphous state but there are few tiny crystalline peaks of relatively low intensity for the film with x ¼ 45 at. %. The chemical composition of the asprepared Bi5GexSe65
x films has been checked using energy dispersive X-ray spectroscopy (EDX). The optical properties for the as-deposited Bi5GexSe65
x thin films have been studied. The additions of Ge content were found to affect the optical constants (refractive index, n and the extinction coefficient, k). Tauc’s relation for the allowed indirect transition is successfully describing the mechanism of the optical absorption. It was found that, the optical energy gap (Eg) decreases with the increase in Ge content. These obtained results were discussed in terms of the chemical bond approach proposed by Bicermo and Ovshinsky. The composition dependence of the refractive index was discussed in terms of the single oscillator model.

The effectofannealinginnitrogenatmosphereonstructuralandelectricalpropertiesofseleniumrich CdSe (SR-CdSe)thinfilmsdepositedbythermalevaporationontoglasssubstrateswerestudied.X-ray diffraction(XRD)patternsshowedthattheas-preparedfilmswereamorphous,whereastheannealed filmswerepolycrystalline.AnalyzingXRDpatternsrevealsthecoexistenceofbothSeandCdSe crystallinephaseswhichexhibitsahexagonalstructure.Themicrostructureparameters(crystallite size, microstrainanddislocationdensity)werecalculatedforannealedfilms. Temperaturedependence(300–500K)ofd.c.conductivitywasstudiedforas-preparedand annealedthinfilms.Theexperimentalresultsindicatethattheelectricalconductiontakingplace throughthermallyactivatedprocess.Athighertemperatures,electricalconductionforas-preparedfilm is takingplaceintheextendedstateswhilelocalizedstatesconductioninthebandtailsismostlikelyto take placeforannealedfilms.Regardingthelowertemperaturerange,conductionbyhoppinginthe localizedstatesneartheFermilevelisfoundtobedominant.Thus,conductivitydatainthisrangewas analyzedusingMott’svariablerangehoppingconduction,whereMott’sparameterswerecalculatedfor SR-CdSe thinfilms.

Structural and optical properties of selenium-rich CdSe (SR-CdSe) thin films prepared by thermal evaporation are studied as a function of annealing temperature. X-ray diffraction (XRD) patterns show that the as-prepared films were amorphous, whereas the annealed films are polycrystalline. Analyzing XRD patterns of the annealed films reveal the coexistence of both (hexagonal) Se and (hexagonal) CdSe crystalline phases. Surface roughness of SR-CdSe films is measured using atomic force microscope (AFM). Analyses of the absorption spectra in the wavelength range (200–2500 nm) of SR-CdSe thin films indicates the existence of direct and indirect optical transition mechanisms. The optical band gap (Eg) of as-prepared film is 1.92 and 2.14 eV for the indirect allowed and direct allowed transitions respectively. After annealing, the absorption coefficient and optical band gap were found to decrease, while the values of refractive index (n) and the extinction coefficient (kex) increase. The dispersion of the refractive index is described using the Wimple–Di Domenico (WDD) single oscillator model and the dispersion parameters are calculated as a function of annealing temperature. Besides, the high frequency dielectric constant (ε∞) and the ratios of the free carrier concentration to its effective mass (N/m*) are studied as a function of annealing temperature. The results are discussed and correlated in terms of amorphous-crystalline transformations.